Medical therapies have been developed that depend on the implantation of devices to selectively stimulate or monitor a patient's nerves or other soft tissue. Functional electrical stimulation of the nervous system, for example, can be used to help to restore or maintain some degree of lost sensory and motor function in neurologically impaired individuals. In addition, there are certain specialized applications, such as the treatment of sleep apnea, where it is necessary to simultaneously monitor and generate electrical signals in nerves. Implantable electrical stimulation and/or recording devices include: (1) surface electrodes placed on the skin surface to activate nerves in a general region of interest; (2) intra muscular and epimysial electrodes to activate nerves to individual muscles; (3) the use of neural interfaces to address individual nerves; and (4) implantable cuff electrodes.
Cuff electrodes have been used for peripheral nerve stimulation and, among other advantages, generally require less energy to produce the desired effects than either surface or intra muscular electrodes. The smaller power requirement may result in a potentially safer long term therapy.
Half cuff electrodes generally have a C-shape cross-section, and cylindrical cuff electrodes can be spiral, helical, split-cylinder, or chambered cylinders. C-shape and split cylinder cuffs generally include a dielectric material defining a bore having sufficient diameter to receive a nerve trunk to be electrically stimulated. One or more contacts on the inner surface of the bore can be used to apply electrical stimuli or monitor nerve activity. The electrical stimuli, for example, may be used to provide functional electrical stimulation, to block neural nerve impulses traveling along the nerve trunk, or to cause other effects.
The spiral type of cuff electrode typically includes a self-curling sheet of non-conductive material biased-curl into a spiral. The spiral cuff also comes off the nerve very easily with a very small amount of force, and can rotate around the nerve, making it difficult to consistently identify and control the desired nerve fascicle. Conductive strips or pads disposed on the self-curling sheet along a line extending peripherally around the inner surface of the cuff. The conductive segments may be electrically conductive for applying electrical impulses or fluid conductive for infusing or extracting medications. In use, a first edge of a self-curling sheet may be disposed adjacent a nerve truck around which the cuff is positioned. The self-curling sheet is permitted to curl around the nerve forming an annular cuff.
The helix or helical cuff, similar to a telephone cord, acts as a spring due to its curved shape and allows a nerve to flex and permits more fluid exchange with surrounding tissue. This cuff must be wrapped around the nerve, which is time consuming and difficult. The helix cuff can be opened and placed over the nerve and there is no closure mechanism, the helix simply closes around the nerve when it is released. The helix cuff can be removed from the nerve, however, very easily and sometimes does not provide the desired proximity to the nerve fascicle of interest.
U.S. Pat. No. 6,456,866 discloses another type of nerve cuff that is particularly useful for functional electrical stimulation. The nerve cuff described in that patent made it easier to precisely position the nerve cuff on a nerve and then to stimulate or monitor selected fibers of the nerves. One application both monitors and generates electrical signals in the hypoglossal nerve for treatment of sleep apnea.